After a hot and humid start to the weekend, a major cold front brought thunderstorms and a drop in temperatures. The pattern which has settled in to start this week is much more autumn-like, with temperatures in the 70’s and lower 80’s and much more comfortable dew points and humidity values. The pattern, however, will turn more volatile by the middle of this upcoming week with multiple storm systems and unsettled weather.

The trend toward more unsettled weather will begin late Monday into Tuesday, as an onshore flow develops and strengthens. Winds will pick up near the area shores, gusting over 25 miles per hour at times as an easterly fetch brings clouds and low level moisture inland from the beaches. This will bring an end to the sunshine which will dominate much of Monday. A mid level disturbance moving northward from the Mid-Atlantic states will aid in the development of showers, spreading into parts of New Jersey from southwest to northeast on Tuesday.

The mid level disturbance which will eventually skirt the East Coast will force the development of a surface low pressure system, a legitimate coastal storm (however weak it may be in pressure terms) with precipitation along the coastal plain. The westward extent of the system, however, will be limited by mid level winds pressing in from the west. So while the easterly flow may continue to bring cloudy and gusty conditions to the coast, with period of rain, the bulk of the steady and heavy rain will remain seaward.

Much of the westerly winds and progressive nature of the pattern keeping the system eastward can be attributed to a large upper level trough and developing system in the Central United States. Forecast models are in good agreement that a significant low pressure system will develop from the North-Central United States toward the Great Lakes and eventually in to Canada. This means that our coastal storm will be shunted off to the east-northeast while weakening.

NAM model showing a major system lifting into Canada later this week with a cold front approaching the Northeast US.

The aforementioned system shifting into Canada will eventually drag a cold front through the area, likely late this week into the early part of the upcoming weekend. The front will be accompanied by showers and possibly a few storms. But the main story will be the air behind it — where 850mb temperatures will fall between 5 and 10 C post-frontal passage. What this means for our area is that autumn will arrive in full force behind the front — with the trough expected to stick around through the medium range.